1. Field of the Invention
The present invention relates to a technique for accommodating an existing low-speed data terminal, and multiplexing cells on a trunk line in a cell transmitting network such as an ATM network, etc., which makes a communication by logically multiplexing and exchanging fixed-length cells.
2. Description of the Related Art
With the popularization of an in-house LAN, the demand for a WAN (Wide Area Network) node device (simply referred to as a node hereinafter) for integrating and accommodating a conventional telephone set or low-speed data terminal and LAN traffic, and dynamically securing a relay bandwidth of the LAN traffic of a high burst nature, has been increasing in recent years.
As a technique for dynamically utilizing a relay bandwidth, an ATM (Asynchronous Transfer Mode) multiplexing technique for logically multiplexing fixed-length cell data, and transmitting each of the multiplexed data, has been reviewed mainly in a broadband field. Recently, this ATM multiplexing technique has been applied also to a narrowband field.
For such a case, a hybrid multiplexing technique for using an existing STM (Synchronous Transfer Mode) dedicated line which can use a multi-access service as a trunk line, and for transmitting ATM cells to be communicated between nodes by using one or a predetermined number of a plurality of time-division channels of the STM dedicated line, was developed. By adopting such a configuration, the ATM multiplexing technique which can flexibly cope with traffic fluctuations and is suitable for a highly efficient transmission can be merged with a TDM (Time Division Multiplexing) technique which can assure a line quality.
Due to the above described technical background, the demand for an ATM switching node which can terminate an ATM trunk line implemented by an ATM dedicated line, or the STM dedicated line which can use a multi-access service, is currently on the rise.
The most important issue to be solved is how to integrally and efficiently accommodate a conventional low-speed data terminal together with a telephone set or LAN traffic, and how to multiplex the LAN traffic on the ATM trunk line in order to maximize the integrated multiplexing effect.
At this time, it is not sufficient only to accommodate a low-speed data terminal efficiently. There is an essential need for providing a value-added service such as a service which makes one terminal continue its communication and makes another terminal abort its communication when a fault occurs on an ATM trunk line.
FIG. 1 is a schematic diagram showing the configuration of a conventional ATM transmitting system for accommodating low-speed data terminals.
Conventionally, when low-speed data from each of a plurality of terminals 103 is received by a terminal IF (interface) unit 104, a cell conversion processing unit 105 converts the low-speed data into ATM cells. In this case, the cell conversion processing unit 105 obtains the VPI/VCI corresponding to each of terminal ports, which is predefined in a terminal port ⇄VPI/VCI conversion table 107; stores the obtained VPI/VCI in the header of each of the ATM cells; and divides the low-speed data and stores the divided low-speed data in the payload of each of the ATM cells. Then, the ATM cells are transmitted from an ATM network transmitting/receiving unit 106 to an ATM trunk line within an ATM network 101.
As described above, with the conventional technique, a single connection path 109 such as a Soft-PVC (a PVC which can be bypassed by software control), a PVC (Permanent Virtual Circuit), or an SVC (Switched Virtual Circuit) which is not shown in this figure, is provided on the ATM trunk line for each opposing connection of each of the plurality of terminals 103.
Therefore, if terminals 103 such as low-speed terminals, whose transmission rates are low in respective communications and which can be accommodated even if their number is large, are accommodated, there is the problem that resources of path identifiers (or cell identifiers) such as VPI/VCI (Virtual Path Identifier/Virtual Channel Identifier) for identifying each of the above described connection paths become insufficient.
The present invention was developed in the above described background, and aims at providing a service which can efficiently accommodate a low-speed data terminal; effectively use path identifiers such as a VPI/a VCI, etc., which are limited resources; perform a relief process to be quickly performed using a bypass route line or a back-up line when a communication cannot be made due to an occurrence of a fault on an ATM trunk line, etc.; and minimize the number of times that a communication between end users is disconnected (released) or a time period during which a communication cannot be made.
The present invention assumes a cell transmitting device (ATM switching node 202) for accommodating a terminal and multiplexing cells on a trunk line in a cell transmitting network (ATM network 201) which logically multiplexes fixed-length cells (ATM cells) and makes a communication.
A bit accommodation pattern table (209) stores the information about bit accommodation patterns when data from a plurality of terminals (203) are accommodated into predetermined multiplexing unit data in bits.
A bit multiplexing/demultiplexing device (bit multiplexing/demultiplexing unit 205) multiplexes the data from each of the plurality of terminals into the predetermined multiplexing unit data by referencing the bit accommodation pattern table, demultiplexes data which is multiplexed into the predetermined multiplexing unit data and is addressed to each of the plurality of terminals, and transmits the demultiplexed data to each of the plurality of terminals.
A cell conversion processing device (cell conversion processing unit 207) performs conversion between predetermined multiplexing unit data processed by a bit multiplexing/demultiplexing device and cells corresponding to a predetermined link.
In the above described configuration of the present invention, the bit multiplexing/demultiplexing device may be adapted to multiplex/demultiplex data corresponding to a terminal belonging to a terminal group into/from the individual multiplexing unit data corresponding to the terminal group for each of a plurality of terminal groups; and a communication controlling device (ATM network transmitting/receiving unit 208, a path identifier conversion table 210, and an S-PVC converting unit 206), which performs different communication control for each of the plurality of terminal groups, may be further included. This communication controlling device performs bypass control of an individual trunk line, for example, for each terminal group when a communication fault occurs. Additionally, this communication controlling device performs bypass control of a trunk line, for example, based on an individual priority for each terminal group when a communication fault occurs. Furthermore, this communication controlling device performs bypass control of a trunk line, for example, based on an individual service category for each terminal group when a communication fault occurs.
In the above described configuration according to the present invention, the cell conversion processing device may be configured to switch a predetermined link corresponding to the cells to be converted/restored into/from predetermined multiplexing unit data to a predefined secondary link, when a communication fault occurs.
Furthermore, the above described configuration of the present invention may further include a table rewriting controlling device (LS unit 313) for changing the connection of a terminal by rewriting the bit accommodation pattern table under a predetermined condition. This table rewrite controlling device rewrites the bit accommodation pattern table, for example, according to a time zone, a day of the week, a date, etc.
Still further, in the above described configuration of the present invention, a point-to-multipoint connection is made by setting the entry for specifying that the data input from a trunk line side is transmitted to the identical or a different trunk line side as it, is in the bit accommodation pattern table; or control is performed in such a way that the data corresponding to a predetermined terminal is bypassed to another terminal or another cell transmitting device, when a fault occurs in the predetermined terminal or on a line of the predetermined terminal.
As described above, according to the present invention, low-speed data from a plurality of terminals, etc. are multiplexed into predetermined multiplexing unit data; and a single predetermined link is established between opposing cell transmitting devices for the multiplexing unit data; and the cells storing the multiplexing unit data are transmitted over the predetermined link. Namely, according to the present invention, a single link can be allocated to the respective connections of a plurality of terminals. Therefore, a low-speed terminal can be efficiently accommodated, and path identifiers such as VPI/VCI, etc., which are limited resources, can be effectively used.
Additionally, according to the present invention, one or a predetermined number of links, whose number is smaller than the number of connections of a plurality of terminals, are allocated to the plurality of terminals, thereby performing customization such as bypass control, a priority operation, a quality assurance operation, etc. for each of the plurality of terminals.
Furthermore, according to the present invention, the worst situation where a communication is entirely disconnected can be prevented by switching to a secondary link or by establishing and connecting a link between a terminal and the opposing cell transmitting device based on call set-up, when a fault occurs on a trunk line.
Still further, according to the present invention, a bit accommodation pattern in a bit accommodation pattern table is rewritten by manual control or automatic control, thereby changing the accommodation configuration of a terminal according to a predetermined condition, for example, according to day, night, or a day of the week, etc.
Still further, according to the present invention, an entry for specifying that the low-data input from a trunk line side is transmitted to an identical or different trunk line side as it is in the bit accommodation pattern table, thereby implementing a point-to-multipoint connection. Or, if a fault occurs on a line of a certain terminal, the data corresponding to the terminal can be bypassed to another terminal or another cell transmitting device.